System And Method To Divert Inductive Energy From Cells

ABSTRACT

A power tool/battery pack combination includes an electric motor, one or more electrochemical cells, and a capacitive element. The electric motor is connected in series to a first switch. The series combination of the electric motor and the first switch is connected to a first terminal and a second terminal. The one or more electrochemical cells are connected across a third terminal and a fourth terminal. The third terminal and the fourth terminal are coupled respectively to the first terminal and the second terminal. The one or more electrochemical cells supply power to the electric motor via the first switch. The capacitive element includes one or more capacitors. The capacitive element is connected across the third terminal and the fourth terminal. The capacitive element is capable of storing inductive energy generated by the one or more electrochemical cells.

FIELD

The present disclosure relates generally to a battery pack and moreparticularly to a technique for diverting inductive energy from thecells of the battery pack away from components connecting the batterypack to a load.

BACKGROUND

Battery packs can be used with a variety of devices. These devicesinclude power tools. Power tools are of many types. Examples of powertools include drills, drill/drivers, hammer drill/drivers, rotaryhammers, screwdrivers, impact drivers, circular saws, jig saws,reciprocating saws, band saws, cut-off tools, cut-out tools, shears,sanders, vacuums, adhesive dispensers, concrete vibrators, staplers,nailers, flashlights, radios, and lasers.

Power tools typically receive electrical power from a wall outlet orfrom the battery pack that is removably coupled to the power tools. Thebattery pack may include one or more electrochemical cells (hereinafter“cells”). The cells can be of different types. For example, the batterypack may include nickel-cadmium (NiCd) cells or lithium-ion (Li-ion)cells.

The power tools typically include a motor and a switch that is used tovary the speed of the motor. During variable speed mode, the switch istypically turned on and off (closed and opened) using pulse widthmodulated signals. The speed of the motor is varied by varying a dutycycle of the pulse width modulated signals. The circuitry that generatesthe pulse width modulated signals may be included in the tool portion orthe battery back portion of the power tool. Some power tools may nothave the variable speed feature and may simply have on/off mode.

One of the electrical characteristics of the cells is that each cell hasan inductance. The value of the inductance depends on the chemicalcomposition and mechanical construction of the cell. Due to theinductance of the cell, an inductive energy builds up in the cell whilethe switch is closed. When the battery or tool switch is turned off, theinductive energy typically dissipates across the tool or battery switchand heats the switch. Depending on the value of the inductance, thefrequency and the duty cycle at which the switch is turned on and off bythe pulse width modulated signal, the heat generated by the inductiveenergy can cause the switch to malfunction.

Therefore, in order to prevent the switch from heating andmalfunctioning, it is desirable to provide a protective device that willdivert the inductive energy from the cells of the battery pack. Theprotective device can prevent the inductive energy from dissipatingacross the switch, thereby preventing the switch from malfunctioning.

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

SUMMARY

In one embodiment, a power tool and battery pack combination comprises apower tool including an electric motor connected in series to a firstswitch. The series combination of the electric motor and the firstswitch is connected to a first terminal and a second terminal. Thecombination also comprises a battery pack including one or moreelectrochemical cells connected across a third terminal and a fourthterminal. The third terminal and the fourth terminal are coupledrespectively to the first terminal and the second terminal. The one ormore electrochemical cells supply power to the electric motor via thefirst switch. A capacitive element including one or more capacitors isconnected across the third terminal and the fourth terminal. Thecapacitive element is capable of storing inductive energy generated bythe one or more electrochemical cells.

The capacitive element prevents the inductive energy from being appliedto the first switch in response to the motor being operated at varyingspeeds. A value of the capacitive element depends on a voltage suppliedby the one or more electrochemical cells and a chemical composition ofthe one or more electrochemical cells. The one or more electrochemicalcells are connected in series, in parallel, or using a combination ofseries and parallel connections. The one or more capacitors areconnected in series, in parallel, or using a combination of series andparallel connections.

The combination further comprises a fuse coupled to the one or morecapacitors. The fuse transforms into an open circuit when one of the oneor more capacitors associated with the fuse malfunctions. Thecombination further comprises a second switch connected in series withthe first switch. The second switch has a higher power rating than thefirst switch. The combination further comprises a controller to controlthe second switch. The controller opens the second switch to stop thesupply of power from the one or more electrochemical cells to theelectric motor when a temperature, voltage, or current of the one ormore electrochemical cells crosses a predetermined threshold. Aninductance of the one or more electrochemical cells is a sum ofinductances of each of the one or more electrochemical cells. A value ofthe inductance depends on a design of the one or more electrochemicalcells.

In another embodiment, a battery pack for supplying power to a powertool comprises a housing. At least one electrochemical cell is containedin the housing. The at least one electrochemical cell has a geometry andis connected across a first terminal and a second terminal of thehousing. A compartment contained in the housing has a geometryequivalent to the geometry of the at least one electrochemical cell. Acapacitive element is contained in the housing. The capacitive elementincludes at least one capacitor. The capacitive element is connectedacross the first terminal and the second terminal of the housing. Thecapacitive element stores inductive energy generated by the at least oneelectrochemical cell. A value of the capacitive element depends on avoltage supplied by the at least one electrochemical cell and a chemicalcomposition of the at least one electrochemical cell. In yet anotherembodiment, there are at least two electrochemical cells and the atleast two electrochemical cells are connected in series, in parallel, orusing a combination of series and parallel connections. There are atleast two capacitors and the at least two capacitors are connected inseries, in parallel, or using a combination of series and parallelconnections.

The battery pack further comprises a fuse coupled to one or morecapacitors of the capacitive element. The fuse transforms into an opencircuit when one of the one or more capacitors associated with the fusemalfunctions. The battery pack further comprises a switch and acontroller that opens the switch to stop the supply of power from the atleast one electrochemical cell to a load when a temperature, voltage, orcurrent of the at least one electrochemical cell crosses a predeterminedthreshold. An inductance of the at least one electrochemical cell is asum of inductances of each of the at least one electrochemical cell. Avalue of the inductance depends on a design of the at least oneelectrochemical cell.

In another embodiment, a battery pack for a power tool comprises acapacitive element, at least one electrochemical cell having a geometry,and a plurality of compartments contained in a housing. Each of thecompartments has a geometry equivalent to the geometry of the at leastone electrochemical cell. The capacitive element and the at least oneelectrochemical cell reside in respective compartments of the batterypack. The capacitive element includes at least one capacitor. Thecapacitive element is connected across a first terminal and a secondterminal of the housing. The capacitive element stores inductive energygenerated by the at least one electrochemical cell.

In another embodiment, a power tool and battery pack combinationcomprises an electric motor arranged in a first housing. The firsthousing includes a first terminal and a second terminal to receive powerto drive the electric motor. At least one electrochemical cell isarranged in a second housing. The second housing includes a thirdterminal and a fourth terminal coupled respectively to the firstterminal and the second terminal of the first housing. The at least oneelectrochemical cell is connected across the third terminal and thefourth terminal. A first switch resides in the first housing. The firstswitch connects the at least one electrochemical cell to the electricmotor responsive to a first control signal. A first controller residesin the first housing. The first controller generates the first controlsignal. A capacitive element resides in the second housing.

The capacitive element includes at least one capacitor. The capacitiveelement is connected across the third terminal and the fourth terminalof the second housing. The capacitive element stores inductive energygenerated by the at least one electrochemical cell thereby preventingthe inductive energy from being applied to the first switch. The atleast one electrochemical cell has a geometry. A plurality ofcompartments is contained in the second housing. Each of the pluralityof compartments has a geometry equivalent to the geometry of the atleast one electrochemical cell. The capacitive element resides in afirst one of the plurality of compartments. The at least oneelectrochemical cell resides in a second one of the plurality ofcompartments. A value of the capacitive element depends on a voltagesupplied by the at least one electrochemical cell and a chemicalcomposition of the at least one electrochemical cell. In yet anotherembodiment, there are at least two electrochemical cells and the atleast two electrochemical cells are connected in series, in parallel, orusing a combination of series and parallel connections. There are atleast two capacitors and the at least two capacitors are connected inseries, in parallel, or using a combination of series and parallelconnections.

The combination further comprises a fuse coupled to one or morecapacitors of the capacitive element. The fuse transforms into an opencircuit when one of the one or more capacitors associated with the fusemalfunctions. The combination further comprises a second switch residingin the second housing. The second switch is connected in series with thefirst switch. The second switch has a higher power rating than the firstswitch. A second controller resides in the second housing. The secondcontroller generates a second control signal when a temperature,voltage, or current of the one or more electrochemical cells crosses apredetermined threshold. The second controller opens the second switchto stop the supply of power from the at least one electrochemical cellto the electric motor based on the second control signal.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a diagram of an exemplary system of power tools;

FIG. 2 is a functional block diagram of a power tool including a batterypack;

FIG. 3 is a functional block diagram of a power tool including a batterypack that has a capacitive element;

FIG. 4A shows different arrangements of capacitors in the capacitiveelement;

FIG. 4B shows different arrangements of electrochemical cells in abattery pack;

FIG. 5A is a functional block diagram of a power tool, where the tooland the battery pack include respective control modules;

FIG. 5B is a functional block diagram of a power tool, where the toolincludes a control module, and where the battery pack does not include acontrol module;

FIG. 5C is a functional block diagram of a power tool, where the batterypack includes a control module, and where the tool does not include acontrol module; and

FIG. 6 is a flowchart of a method for diverting inductive energy fromcells of a battery pack to a capacitive element connected across thebattery pack.

FIGS. 7A-7F show an example of an arrangement of electrochemical cellsand the capacitive element in the battery pack.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

FIG. 1 shows a system 10 of power tools. The system 10 of power toolscan include, for example, one or more power tools 12, a battery pack 16,and a battery pack charger 18. Each of the power tools 12 can be anytype of power tool, including without limitation drills, drill/drivers,hammer drill/drivers, rotary hammers, screwdrivers, impact drivers,circular saws, jig saws, reciprocating saws, band saws, cut-off tools,cut-out tools, shears, sanders, vacuums, adhesive dispensers, concretevibrators, staplers, nailers, flashlights, radios, and lasers.

In the example shown, the system 10 of power tools includes a firstpower tool 12 a and a second power tool 12 b. For example, the firstpower tool 12 a can be a drill/driver similar to that which is describedin U.S. Pat. No. 6,431,289, while the second power tool 12 b can be acircular saw similar to that which is described in U.S. Pat. No.6,996,909. The battery pack 16 can be selectively removably coupled tothe first and second power tools 12 a and 12 b to provide electricalpower thereto. Except as otherwise described herein, the battery pack 16can be configured in a manner that is similar to that which is describedin U.S. Pat. Nos. 7,273,759 and 7,508,171. The battery pack 16 can alsobe selectively electrically coupled to the battery pack charger 18 tocharge the battery pack 16. It is noteworthy that the broader aspects ofthis disclosure are applicable to battery packs for other types ofbattery powered devices (e.g., flashlights, radios, and lasers).

FIG. 2 shows an embodiment of a power tool/battery pack combination 100including a battery pack that does not have a capacitive element. Thecombination 100 includes a power tool 102 and a battery pack 104. Thepower tool 102 and the battery pack 104 may be enclosed in separatehousings. The power tool 102 includes a motor 106 and a switch 108. Afreewheeling diode 110 may be connected across the motor 106. While notshown, a freewheeling diode may be connected across the battery pack 104as well, to handle cases, for example, where the power tool has nofreewheeling diode and the motor's inductive energy could damage aswitch in the battery pack 104.

The battery pack 104 includes one or more electrochemical cells(hereinafter cells) 112 and may include a switch 114. The cells 112 maybe connected to each other in series, in parallel, or using acombination of series and parallel connections. Each of the cells 112has an intrinsic inductance. An effective inductance of the cells 112 isshown as an inductance 116 connected in series with the cells 112. Theinductance 116 shown is an intrinsic inductance of the cells 112 and isshown externally connected to the cells 112 for illustrative purposesonly.

In use, the battery pack 104 is connected to the power tool 102. Thecells 112 supply power to the motor 106 through the switches 114 and108. The switch 114 is closed when the power tool 102 is operated. Theswitch 114 can be opened and the power supply from the cells 112 to themotor 106 can be disconnected when a sensor (not shown for simplicity ofillustration) senses that a temperature, voltage, or current of one ormore cells 112 crosses a predetermined threshold. The switch 108 can beoperated to vary the speed of the motor 106. For example, the switches114 and 108 may be further defined as field effect transistors (FETs).The switch 108 may be driven by pulse width modulated signals having aduty cycle. The speed of the motor 106 can be varied by varying the dutycycle of the pulse width modulated signals. The switch 108 can also bein bypass mode, where the PWM circuit is not in use (e.g., if thetrigger of the power tool 102 is fully depressed).

While the speed of the motor 106 is varied, each time the switch 108turns on (closes), the inductive energy that is already built up in thecells 112 when the switch 108 is turned off, typically dissipates acrossthe switch 108, thereby heating the switch 108. The inductive energy mayalso dissipate across the switch 114 and/or other circuit components.Depending on the value of the inductance 116 of the cells 112 anddepending on the duty cycle at which the switch 108 is turned on andoff, the switch 108 (and/or other circuit components) can heatexcessively and/or malfunction. The value of the inductance 116 dependsprimarily on the design and construction of the cells 112.

FIG. 3 shows an embodiment of a power tool/battery pack combination 200including a battery pack that has a capacitive element. The combination200 includes the power tool 102 and a battery pack 204. The battery pack204 includes all of the components of the battery pack 104.Additionally, the battery pack 204 includes a capacitive element 206.The capacitive element 206 may include one or more capacitors. Thecapacitors may be connected to each other in series, in parallel, orusing a combination of series and parallel connections. While the speedof the motor 106 is varied, each time the switch 108 turns off, thecapacitors store the inductive energy generated by the cells 112,thereby preventing the inductive energy from being applied to the switch108.

The inductive energy is dissipated at a natural frequency of an RLCcircuit formed by the capacitive element 206, the inductance of thecells 112, and the internal resistance of the circuitry. The use of thecapacitive element 206 is not restricted to power tools with variablespeed. The capacitive element 206 can also be used with power tools thatare simple on/off type. When an on/off type power tool shuts off, thecapacitive element 206 can be used to absorb the inductive energygenerated by the cells to prevent damage to control circuitry of theon/off type power tool. In general, the capacitive element 206 can beused to protect any switch in a high current path in a circuit.

The value (i.e., the capacitance) of the capacitive element 206 maydepend on the voltage rating of the cells 112. In addition, the value ofthe capacitive element 206 may depend on the chemical composition andmechanical construction of the cells 112. Each capacitor in thecapacitive element 206 may have a different value. Alternatively, all ofthe capacitors in the capacitive element 206 may have the same value.

For example, consider a battery and tool system, where a certain amountof energy J needs to be diverted to the capacitive element 206. Theenergy, J, may be the avalanche energy of a MOSFET when the MOSFET opens(turns off). The capacitance C of the capacitive element 206 can beestimated by the maximum energy stored by a capacitor: J=½CV², where Cis the capacitance of the capacitor (the capacitive element 206), and Vis the voltage across the capacitor when the energy absorption needs tooccur. According to the present disclosure, the required capacitance ofthe capacitive element 206 is primarily a function of the inductance ofeach of the cells 112.

Suppose a battery with a first cell arrangement (e.g., 20v at 4v percell) has a total inductance of L and an already determined capacitanceC for the capacitive element 206. Assuming the same cell is used, abattery with a second cell arrangement (e.g., 16v at 4v per cell) wouldhave 80% of the inductance first cell arrangement, and a correspondingcapacitance requirement of approximately 0.80*C. A third cellarrangement (e.g., 12v at 4v per cell) would have 60% of the first cellarrangement, and a corresponding capacitance requirement ofapproximately 0.60*C. Because the inductance is halved when cells areconnected in parallel, the first cell arrangement employing cellsconnected in parallel with the same cell and tool system wouldtheoretically require 2*C capacitance, the second cell arrangementemploying cells connected in parallel with the same cell and tool systemwould require 0.8*2*C capacitance, and so on.

A fuse may be associated with one or more capacitors in the capacitiveelement 206. In the event that a capacitor malfunctions, the fuseassociated with the malfunctioning capacitor may open therebytransforming the malfunctioning capacitor into an open circuit, therebyeffectively removing the malfunctioning capacitor from the circuit. FIG.4A (described below) shows an example arrangement including the fuse.

The housing of the battery pack 204 may include a plurality ofcompartments. Each compartment may have the same geometry. The cells 112may reside in one or more of the compartments. That is, each of thecells 112 resides in a respective one of the compartments. Thecapacitive element 206 can reside in any of the compartments where oneof the cells 112 can reside instead. In other words, the compartment inwhich the capacitive element 206 resides has the same geometry as thecompartment in which one of the cells 112 resides. Accordingly, one ofthe cells 112 can be removed from its compartment and can be substitutedwith an element having the same geometry as the cell, where the elementhouses the capacitive element 206. The electrical connections across thecompartments are arranged in such a manner so that the capacitiveelement 206 is connected across (i.e., in parallel to) the cells 112.

In some implementations, the capacitive element 206 may not have theshape of a cell and may not have the same geometry as the compartment inwhich one of the cells 112 resides. Rather, the capacitive element 206may simply comprise a PCB and could reside anywhere in the battery pack204.

FIG. 4A shows examples of different arrangements that may be used toconnect the capacitors in the capacitive element 206. For example, inthe arrangement 206-1, the capacitors may be connected to each other inseries to form the capacitive element 206. As another example, in thearrangement 206-2, the capacitors may be connected to each other inparallel to form the capacitive element 206. Alternatively, acombination of series and parallel connections of the capacitors may beused to form the capacitive element 206. In some implementations, thecapacitive element 206 may be connected across each of the cells 112.

FIG. 4B shows examples of different arrangements that may be used toconnect the cells 112. For example, in the arrangement 112-1, two ormore cells may be connected to each other in series to form the cells112. As another example, in the arrangement 112-2, two or more cells maybe connected to each other in parallel to form the cells 112.Alternatively, a combination of series and parallel connections of cellsmay be used to form the cells 112.

FIG. 5A shows an alternative embodiment of a power tool/battery packcombination 300, where the tool and the battery pack include respectivecontrol modules. The combination 300 includes a power tool 302 and abattery pack 304. The power tool 302 includes all of the components ofthe power tool 102. Additionally, the power tool 302 includes a toolcontrol module 306 and one or more sensors 308. The tool control module306 generates control signals to control the switch 108. For example,the control signals may include pulse width modulated signals.

The sensors 308 may sense one or more conditions associated with one ormore components of the tool 302. For example, one of the sensors 308 maysense a parameter associated with the motor 106. For example, theparameter may include a temperature of the motor 106, current throughthe motor 106, and so on. As another example, another one of the sensors308 may sense a parameter associated with the switch 108. For example,the parameter may include a temperature of the switch 108, currentthrough the switch 108, voltage across the switch 108, and so on.

The sensors 308 may output signals indicating the conditions of thecomponents of the tool 302 to the tool control module 306. The toolcontrol module 306 may control the switch 108 based on the conditions ofthe components of the tool 302. For example, the tool control module 306may disable the switch 108 and stop power supply from the cells 112 tothe motor 106 if the temperature of the motor 106 and/or the temperatureof the switch 108 crosses a predetermined threshold.

The battery pack 304 may include all of the components of the batterypack 204. Additionally the battery pack 304 may include a battery packcontrol module 310 and one or more sensors 312. The sensors 312 maysense one or more conditions of the components of the battery pack 304.For example, the sensors 312 may sense one or more conditions of thecells 112 and the capacitive element 206. For example, one of thesensors 312 may sense the temperature of the cells 112. Additionally,the sensors 312 may sense the voltage and/or current supplied by thecells 112. Further, the sensors 312 may sense the number of capacitorsoperating in the capacitive element 206 at a given time. For example,the number of capacitors operating in the capacitive element 206 at agiven time may depend on the number of open circuit fuses at a giventime. In addition, the presence of the capacitive element 206 can besensed through an end of line test at the manufacturing facility.

The sensors 312 may output signals indicating the conditions of thecells 112 and the capacitive element 206 to the battery pack controlmodule 310. The battery pack control module 310 may control the switch114 based on the conditions of the components of the battery pack 304.For example, the battery pack control module 310 may disable the switch114 and stop power supply from the cells 112 to the motor 106 if thetemperature of the cells 112 crosses a predetermined threshold, thenumber of open circuit fuses exceeds a predetermined number, or thevoltage and/or current of the cells 112 drops below a predeterminedthreshold.

FIG. 5B is a functional block diagram of a power tool 400, where thetool includes a control module, and where the battery pack does notinclude a control module. The power tool 400 includes the tool 302 andthe battery pack 204. The tool 302 operates as described with referenceto FIG. 5A. The battery pack 204 operates as described with reference toFIG. 3 with the exception of performing functions related to the switch114.

Additional configurations of the tool and the battery pack arecontemplated. For example, in one configuration, a control module thatcontrols the motor and the switch in the tool may be included in thebattery pack instead of in the tool. FIG. 5C shows such a configuration.In FIG. 5C, a functional block diagram of a power tool 450 is shown,where the battery pack includes a control module, and where the tooldoes not include a control module. The power tool 450 includes the tool102 and the battery pack 304. The tool 102 operates as described withreference to FIGS. 2 and 3. The battery pack 304 operates as describedwith reference to FIG. 4A and additionally performs the functions of thetool control module 306 shown in FIG. 5B. Further, the presentdisclosure uses the switches 108 and 114 only as examples of circuitcomponents that may be protected using the capacitive element 206. Thecapacitive element 206 may be used to protect other circuit componentsfrom the inductive energy of the cells 112. In some embodiments, thecapacitor array may be integrated into the power tool and not in aseparate battery pack. That is, the battery may reside in the powertool.

FIG. 6 is a flowchart of a method 500 for operating a power tool bydiverting inductive energy from cells of a battery pack to a capacitiveelement connected across the battery pack. At 502, a user varies thespeed of the tool motor. At 504, when the speed of the tool motor isbeing varied (or when a simple on/off tool is turned off, or when thetool trigger is fully depressed in bypass mode and is released), themethod 500 diverts inductive energy generated by the cells to thecapacitive element connected across the cells, thereby preventingexcessive inductive energy from being applied across the tool switch. Insome implementations, at 506, the method 500 senses one or moreconditions of one or more components of the battery pack and/or thetool. At 508, the method determines if a condition of a component of thebattery pack and/or the tool is within a predetermined range. The method500 returns to 502 if the conditions of the components of the batterypack and the tool are within the respective predetermined ranges. At510, if a condition of a component of the battery pack and/or the toolis not within a predetermined range, the method 500 stops the powersupply from the cells to the tool motor.

FIGS. 7A-7F show an example of an arrangement of electrochemical cellsand the capacitive element in the battery pack. In FIG. 7A, a batterypack (e.g., battery pack 204 or 304) including a capacitive element(e.g., capacitive element 206) according to the present disclosure isshown. In FIG. 7B, the battery pack includes the cells 112 and thecapacitive element 206. In FIGS. 7C-7E, the capacitive element 206 isshown in detail. In particular, the geometry of the capacitive element206 is the same as that of any of the cells 112. In FIG. 7F, thecapacitive element 206 is shown coupled to the cells 112.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A or Bor C), using a non-exclusive logical OR. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.

In this application, including the definitions below, the term modulemay be replaced with the term circuit. The term module may refer to, bepart of, or include an Application Specific Integrated Circuit (ASIC); adigital, analog, or mixed analog/digital discrete circuit; a digital,analog, or mixed analog/digital integrated circuit; a combinationallogic circuit; a field programmable gate array (FPGA); a processor(shared, dedicated, or group) that executes code; memory (shared,dedicated, or group) that stores code executed by a processor; othersuitable hardware components that provide the described functionality;or a combination of some or all of the above, such as in asystem-on-chip.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared processor encompasses a single processorthat executes some or all code from multiple modules. The term groupprocessor encompasses a processor that, in combination with additionalprocessors, executes some or all code from one or more modules. The termshared memory encompasses a single memory that stores some or all codefrom multiple modules. The term group memory encompasses a memory that,in combination with additional memories, stores some or all code fromone or more modules. The term memory may be a subset of the termcomputer-readable medium. The term computer-readable medium does notencompass transitory electrical and electromagnetic signals propagatingthrough a medium, and may therefore be considered tangible andnon-transitory. Non-limiting examples of a non-transitory tangiblecomputer readable medium include nonvolatile memory, volatile memory,magnetic storage, and optical storage.

The apparatuses and methods described in this application may bepartially or fully implemented by one or more computer programs executedby one or more processors. The computer programs includeprocessor-executable instructions that are stored on at least onenon-transitory tangible computer readable medium. The computer programsmay also include and/or rely on stored data.

1. A power tool and battery pack combination comprising: a power toolincluding an electric motor connected in series to a first switch, theseries combination of the electric motor and the first switch connectedto a first terminal and a second terminal; and a battery pack includingone or more electrochemical cells connected across a third terminal anda fourth terminal, the third terminal and the fourth terminal coupledrespectively to the first terminal and the second terminal, wherein theone or more electrochemical cells supply power to the electric motor viathe first switch; and a capacitive element including one or morecapacitors, the capacitive element connected across the third terminaland the fourth terminal, the capacitive element capable of storinginductive energy generated by the one or more electrochemical cells. 2.The combination of claim 1 wherein the capacitive element prevents theinductive energy from being applied to the first switch in response tothe motor being operated at varying speeds.
 3. The combination of claim1 wherein a value of the capacitive element depends on a voltagesupplied by the one or more electrochemical cells and a chemicalcomposition of the one or more electrochemical cells.
 4. The combinationof claim 1 wherein: the one or more electrochemical cells are connectedin series, in parallel, or using a combination of series and parallelconnections; and the one or more capacitors are connected in series, inparallel, or using a combination of series and parallel connections. 5.The combination of claim 1 further comprising a fuse coupled to the oneor more capacitors, wherein the fuse transforms into an open circuitwhen one of the one or more capacitors associated with the fusemalfunctions.
 6. The combination of claim 1 further comprising: a secondswitch connected in series with the first switch, wherein the secondswitch has a higher power rating than the first switch; and a controllerto control the second switch, wherein the controller opens the secondswitch to stop supply of power from the one or more electrochemicalcells to the electric motor when a temperature, voltage, or current ofthe one or more electrochemical cells crosses a predetermined threshold.7. The combination of claim 1 wherein: an inductance of the one or moreelectrochemical cells is a sum of inductances of each of the one or moreelectrochemical cells; and a value of the inductance depends on a designof the one or more electrochemical cells.
 8. A battery pack forsupplying power to a power tool, the battery pack comprising: a housinghaving a first terminal and a second terminal and configured todetachable couple to the power tool; at least one electrochemical cellcontained in the housing, a given electrochemical cell having a givenshape and connected across the first terminal and the second terminal ofthe housing; a compartment container contained in the housing, thecontainer having a shape equivalent to the given electrochemical cellwith dimensions equal to the given shape of the given electrochemicalcell; and two or more capacitors electrically coupled together andcontained in the container, where the two or more capacitors areconnected across the first terminal and the second terminal of thehousing.
 9. The battery pack of claim 8 wherein the two or morecapacitors store inductive energy generated by the at least oneelectrochemical cell.
 10. The battery pack of claim 8 wherein a value ofthe two or more capacitors depend on a voltage supplied by the at leastone electrochemical cells and a chemical composition of the at least oneelectrochemical cells.
 11. The battery pack of claim 8 wherein: thereare at least two electrochemical cells and the at least twoelectrochemical cells are connected in series, in parallel, or using acombination of series and parallel connections; and there are at leasttwo capacitors and the at least two capacitors are connected in series,in parallel, or using a combination of series and parallel connections.12. The battery pack of claim 8 further comprising a fuse coupled to thetwo or more capacitors, wherein the fuse transforms into an open circuitwhen one of the two or more capacitors associated with the fusemalfunctions.
 13. The battery pack of claim 8 further comprising: aswitch; and a controller that opens the switch to stop supply of powerfrom the at least one electrochemical cells to a load when atemperature, voltage, or current of the at least one electrochemicalcells crosses a predetermined threshold.
 14. The battery pack of claim 8wherein: an inductance of the at least one electrochemical cells is asum of inductances of each of the at least one electrochemical cells;and a value of the inductance depends on a design of the at least oneelectrochemical cells.
 15. A battery pack for a power tool, the batterypack comprising: a capacitive element; at least one electrochemicalcell, the at least one electrochemical cell having a geometry; and aplurality of compartments contained in a housing, each of thecompartments having a geometry equivalent to the geometry of the atleast one electrochemical cell, wherein the capacitive element and theat least one electrochemical cell reside in respective compartments ofthe battery pack.
 16. The battery pack of claim 15 wherein thecapacitive element includes at least one capacitor, wherein thecapacitive element is connected across a first terminal and a secondterminal of the housing, and wherein the capacitive element storesinductive energy generated by the at least one electrochemical cell. 17.A power tool and battery pack combination comprising: an electric motorarranged in a first housing, the first housing including a firstterminal and a second terminal to receive power to drive the electricmotor; at least one electrochemical cell arranged in a second housing,the second housing including a third terminal and a fourth terminalcoupled respectively to the first terminal and the second terminal ofthe first housing, the at least one electrochemical cell connectedacross the third terminal and the fourth terminal; a first switchresiding in the first housing, the first switch connecting the at leastone electrochemical cell to the electric motor responsive to a firstcontrol signal; a first controller residing in the first housing, thefirst controller generating the first control signal; and a capacitiveelement residing in the second housing.
 18. The combination of claim 17wherein the capacitive element includes at least one capacitor, whereinthe capacitive element is connected across the third terminal and thefourth terminal of the second housing, and wherein the capacitiveelement stores inductive energy generated by the at least oneelectrochemical cell thereby preventing the inductive energy from beingapplied to the first switch.
 19. The combination of claim 17, wherein:the at least one electrochemical cell has a geometry; a plurality ofcompartments contained in the second housing, each of the plurality ofcompartments having a geometry equivalent to the geometry of the atleast one electrochemical cell; the capacitive element resides in afirst one of the plurality of compartments; and the at least oneelectrochemical cell resides in a second one of the plurality ofcompartments.
 20. The combination of claim 17 wherein a value of thecapacitive element depends on a voltage supplied by the one or moreelectrochemical cells and a chemical composition of the one or moreelectrochemical cells.
 21. The combination of claim 17 wherein: thereare at least two electrochemical cells and the at least twoelectrochemical cells are connected in series, in parallel, or using acombination of series and parallel connections; and there are at leasttwo capacitors and the at least two capacitors are connected in series,in parallel, or using a combination of series and parallel connections.22. The combination of claim 17 further comprising a fuse coupled to oneor more capacitors of the capacitive element, wherein the fusetransforms into an open circuit when one of the one or more capacitorsassociated with the fuse malfunctions.
 23. The combination of claim 17further comprising: a second switch residing in the second housing,wherein the second switch is connected in series with the first switch,wherein the second switch has a higher power rating than the firstswitch; and a second controller residing in the second housing, thesecond controller generating a second control signal when a temperature,voltage, or current of the one or more electrochemical cells crosses apredetermined threshold, wherein the second controller opens the secondswitch to stop supply of power from the one or more electrochemicalcells to the electric motor based on the second control signal.